Re: [PATCH v4 58/59] acpi: Add more documentation for struct acpi_gpio

On Tue, Sep 22, 2020 at 12:45:43PM -0600, Simon Glass wrote:

Add some documentation provided by Andy Shevchenko to describe how to use struct acpi_gpio.

Thanks!

I see Bin already applied this, perhaps follow up fix is needed. See below.

...

• • Note that GpioIo doesn't have any means of Active Low / High setting, so a

GpioIo -> GpioIo()

• • _DSD must be provided to mitigate this.

Plus the following:

"This parameter does not make sense for GpioInt() since it has its own means to define it."

• • GpioIo doesn't properly communicate the initial state of the output pin,

GpioIo -> GpioIo()

• • thus Linux assumes the simple rule:
• • Pull Bias Polarity Requested...
• • Implicit x AS IS (assumed firmware configured for us)
• • Explicit x (no _DSD) as Pull Bias (Up == High, Down == Low),

• •                           assuming non-active (Polarity = !Pull Bias)
    

• • Down Low as low, assuming active

• • Down High as high, assuming non-active

Should be read:

" * Down High as low, assuming non-active"

• • Up Low as high, assuming non-active
• • Up High as high, assuming active
• • GpioIo() can be used as interrupt and in this case the IoRestriction mustn't
• • be OutputOnly.
• • It also requires active_low flag from _DSD in cases where it's
• • needed (better to always provide than rely on above assumption made on OS
• • level).